A conceptual model is proposed in this study to describe the threshold conditions of rainfall-induced shallow landslides with cracks. Landslides occur only when the rainfall intensity exceeds the threshold value, which depends on the characteristics of cracks. The total rainfall needed to trigger the landslide decreases with increasing rainfall intensity. This model fits well previous regression curves for debris flows. Moreover, the effects of cracks on the threshold conditions can be evaluated in the present model. The rainfall intensity required for landslides to occur increases when cracks get deeper. although the rainfall duration becomes shorter. Consequently, the scenarios of large shallow landslides occur around the peaks of rainfalls.